Diagnostic cutoff points for sarcopenia in chest computed tomography (CT) have not been established although CT is widely used for investigating skeletal muscles. This study aimed to determine reference values for sarcopenia of thoracic skeletal muscles acquired from chest CT scans and to analyze variables related to sarcopenia using the cutoff values determined in a general Asian population. We retrospectively reviewed chest CT scans of 4470 subjects (mean age 54.8 ± 9.9, 65.8% male) performed at one check-up center in South Korea from January 2016 to August 2017. We measured the cross-sectional area (CSA) of the pectoralis, intercostalis, paraspinal, serratus, and latissimus muscles at the 4th vertebral region (T4CSA) and pectoralis muscle area (PMCSA) at the 4th vertebral region. Sarcopenia cutoff was defined as sex-specific values of less than -2 SD below the mean for a healthy and younger person (n=335, age 19-39 years). T4CSA and PMCSA cutoffs for sarcopenia were 100.06cm2 and 29.00cm2 in males, and 66.93cm2 and 18.29cm2 in females. The prevalence of sarcopenia in men and women were 11.9% (319/2690) and 10.7% (154/1445) using T4CSA cutoff and 6.2% (168/2690) and 12.8% (185/1445) using PMCSA cutoff. In the multivariate logistic regression model, sarcopenia defined by T4CSA was related to older age [odds ratio (95% confidence interval): 1.09 (1.07-1.11)] and diabetes [1.66 (1.14-2.25)], and was inversely related to body mass index (BMI) [0.80 (0.76-0.84)] and sufficient physical activity [0.65 (0.49-0.86)]; sarcopenia defined by PMCSA was related to older age [1.08 (1.06- 1.10)], hypertension [1.43 (1.04-1.97)], diabetes [1.64 (1.13-2.40)], history of cancer [1.66 (1.05-2.62)], alcohol consumption [1.01 (1.00-1.02)], and was inversely related to male sex [0.34 (0.21-0.54)], BMI [0.93 (0.88-0.98)], and sufficient physical activity [0.62 (0.45-0.86)]. Reference cutoff values of a general population reported here will enable sex-specific standardization of thoracic muscle mass quantification and sarcopenia assessment.